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It is a fatty acid that is found naturally in various animal and vegetable fats and oils. It is a colorless and odorless oil, although commercial samples may be yellowish.
Oleic acid is a non-essential fatty acid , which means that it is produced naturally by the human body.
In chemical terms, oleic acid is classified as a monounsaturated omega-9 fatty acid. Monounsaturated fats have only one double bond and are defined by the number of carbons in their omega side chain.
Oleic acid is sometimes abbreviated as (C18: 1), referring to its carbon structure. It has the formula CH3 (CH2) 7CH = CH (CH2) 7COOH.
Most naturally occurring monounsaturated fats have the cis isomer conformation, which refers to the orientation of the double bond. Artificially produced trans isomers are associated with negative health outcomes.
The term ” oleic ” means related to, or derived from, olive oil, which is composed primarily of triglycerides rich in oleic acid.
Function
Olive oil is the largest dietary contributor to human consumption of omega-9 monounsaturated fats.
It is the main member of the omega-9 class of monounsaturated fatty acids. Oleic acid accounts for 92% of the cis isomeric monounsaturated fats in the human diet.
Fatty acids (or their salts) do not usually appear as such in biological systems.
Instead, fatty acids like oleic acid occur as their esters, commonly triglycerides, which are the fatty materials in many natural oils. Fatty acids can be obtained by saponification of triglycerides.
Oleic acid triglycerides comprise the majority of olive oil. Free oleic acid makes olive oil inedible. It also composes:
- 59-75% walnut oil.
- 61% acceptance of canola.
- 36-67% peanut oil.
- 60% macadamia oil.
- 20-85% sunflower oil (the latter in the high oleic acid variant).
- 15 -20% grapeseed oil.
It also comprises 22.18% of the fats of the fruit of the Durio graveolens species, sea buckthorn oil and sesame oil, and 14% poppy seed oil.
It is abundantly present in many animal fats, constituting 37 to 56% chicken and turkey fat and 44 to 47% lard.
Oleic acid is the most abundant fatty acid in human adipose tissue, and the second most abundant in human tissues in general, only for palmitic acid.
Like an insect pheromone
Oleic acid is emitted from the decaying carcasses of a number of insects, including Pogonomyrmex bees and ants, and triggers the instincts of living workers to remove corpses from the hive.
If a live bee or ant is cleaned with oleic acid, it is dragged away to be disposed of as if it were dead.
The smell of oleic acid can also indicate danger to living insects, leading them to avoid others that have succumbed to the disease or places where predators lurk.
Drug interactions
Oleic acid has potential interactions with blood pressure medications or diabetes medications. When taken with one of these drugs, the combined effect can cause blood pressure or blood sugar levels to drop too low.
Some chemotherapy treatments for breast cancer (paclitaxel) can be enhanced (increased cell death) in the presence of high levels of oleic acid and its derived compounds when studied in cells.
Nutritional supplements
Most adults get enough oleic acid in their normal diet.
However, you may consider a supplement to increase oleic acid in your diet if you are interested in one of its positive health effects.
For some patients with high blood pressure (hypertension), olive oil or oleic acid supplements can be as effective as recipes in lowering blood pressure.
Olive leaf extracts and other olive supplements are often normalized for their oleuropein content to indicate what portion of the supplement is derived from olives.
Olive oil
The recommended dose for dietary supplementation for patients with high blood pressure is 2 to 4 tablespoons of olive oil, or 10 to 20 olives per day.
Olive leaf extract
Olive leaf extract supplements have also been effective in lowering blood pressure in a twin comparison study. The recommended dose is 500 mg twice a day.
Other Common High Oleic Acid Supplements
The following oils and extracts are often sold as oils or in capsules. Vegetable oil blends are also common.
Omega complex (usually a mixture of omegas-3, 6 and 9). Note that “essential omega” or “essential fatty acid” supplements often contain only omega-3 and omega-6, not omega-9.
Macadamia oil, sesame oil, rice bran oil, and other vegetable oils (coconut, safflower, etc.) also contain oleic acid, but in smaller amounts.
Mechanism of action
Oleic acid plays an active role in many body processes by changing the composition of the cell membrane and altering the receptors that are present on the membrane as a result.
By changing the presence of the receptor on the cell membrane, oleic acid has the following effects:
- It blocks the transport of cholesterol in the small intestine by reducing the production of cholesterol receptors.
- Increases the production of protective factors of the heart (platelet aggregation and hemostatic factors).
- Increases protein production to promote healthy blood vessel function (PKA and RhoA).
- Helps immune cells (neutrophils) in identifying inflammation. This leads to a faster immune response and faster resolution of inflammation, including inflammation-related symptoms such as pain.
Oleic acid also serves several functions in the regulation of neurotransmitters:
- It blocks the reuptake of gamma-aminobutyric acid (GABA), increasing the concentration of gamma-aminobutyric acid outside the cell, which in turn increases the associated nerve transmission in the brain.
- It competes with serotonin for receptor binding to reduce excess serotonin activity in the gut. Dopamine forms a product with oleic acid that is necessary for body movement (locomotion).
- A higher level of oleic acid in the cell membrane reduces oxidative damage caused by free radicals.
- Oleic acid is an important building block of the brain and nervous system. It is required for the formation of myelin and for nerve growth and repair.
Production and chemical behavior
Oleic acid biosynthesis involves the action of the enzyme stearoyl-CoA 9-desaturase that acts on stearoyl-CoA. In effect, the stearic acid is dehydrogenated to give the derived monounsaturated oleic acid.
Oleic acid undergoes the reactions of carboxylic acids and alkenes. It is soluble in aqueous base to give soaps called oleates. The iodine is added through the double bond. Hydrogenation of the double bond produces the saturated derivative stearic acid.
Double bond oxidation occurs slowly in air, and is known as rancidification in food products or drying in coatings.
Reduction of the carboxylic acid group produces oleyl alcohol. Oleic acid ozonolysis is an important pathway for azelaic acid. The by-product is nonanoic acid:
- H17C8CH = CHC7H14CO2H + 4 «O» → H17C8CO2H + HO2CC7H14CO2H.
Azelaic acid esters have applications in lubrication and plasticizers.
Related compounds
The stereoisomer of oleic acid is called elaidic acid or trans-9-octadecenoic acid. These isomers have different physical and biochemical properties.
Elaidic acid, the most abundant trans fatty acid in the diet, appears to have an adverse effect on health. A reaction that converts oleic acid to elaidic acid is called elaidinization.
Another isomer of oleic acid that occurs naturally is petroselinic acid.
In chemical analysis, fatty acids are separated by gas chromatography from their derivatives of methyl esters. Alternatively, the separation of unsaturated isomers is possible by silvering thin layer chromatography.
Applications
The main use of oleic acid is as a component in many foods, in the form of triglycerides. It is a component of the normal human diet as part of animal fats and vegetable oils.
Oleic acid as its sodium salt is a main component of soap as an emulsifying agent. It is also used as an emollient. Small amounts of oleic acid are used as an excipient in pharmaceutical products, and it is used as an emulsifying or solubilizing agent in aerosol products.
Niche uses
Oleic acid is also used to induce lung damage in certain types of animals, for the purpose of testing new drugs and other means of treating lung diseases.
Specifically in sheep, intravenous administration of oleic acid causes acute lung injury with corresponding pulmonary edema.
This type of research has been of particular benefit to preterm infants, for whom the treatment of underdeveloped lungs (and associated complications) is often a matter of life and death.
Oleic acid is used as a solder flux in stained glass work to bind lead.
Oleic acid is also widely used in solution phase synthesis of nanoparticles, which functions as a kinetic control to control the size and morphology of nanoparticles.
Health effects
Oleic acid is a common monounsaturated fat in the human diet.
Consumption of monounsaturated fats has been associated with a decrease in low-density lipoprotein (LDL) cholesterol and possibly an increase in high-density lipoprotein (HDL) cholesterol.
However, its ability to raise high-density lipoproteins is still debated.
Oleic acid may be responsible for the hypotensive (blood pressure lowering) effects of olive oil.
Adverse effects have also been documented, however, as levels of oleic and monounsaturated fatty acids in the membranes of red blood cells have been associated with an increased risk of breast cancer, although consumption of oleate in olive oil It has been associated with a lower risk of breast cancer.
Oleic acid in olive oil and the Mediterranean diet
Olive oil is an important component of the Mediterranean diet.
In Mediterranean countries, olive oil is the main source of monounsaturated fats in the diet.
This compares to the United States and northern European countries where meat and dairy products (20 to 40% monounsaturated fat on average) are more common dietary sources, and also include higher levels of saturated fat.
The Mediterranean diet has been linked to a variety of health benefits, including better heart health, lower blood pressure, lower rates of obesity, and a lower incidence of type 2 diabetes.
Oleic acid is responsible for some of the health benefits of this diet, but other potentially beneficial compounds in olive oil (squalene, antioxidant phenolic alcohols, polyphenols, and vitamin E) also contribute to these benefits.
Health benefits of oleic acid
Oleic acid lowers cholesterol
Patients at risk for heart disease were often prescribed a low-fat, high-carbohydrate diet. Both the high carbohydrate diet and a high monounsaturated fat diet lowered total blood cholesterol levels.
However, patients on the high monounsaturated fat diet saw lower low-density lipoproteins: cholesterol and triglycerides than did those on the carbohydrate diet.
Cells in the small intestine absorbed less cholesterol when oleic acid was present, because fewer proteins were produced to transport cholesterol.
Oleic acid protects against heart disease
The famous “seven-country study” followed Mediterranean men and women for many decades and compared them with their counterparts in Northern Europe, Japan, and the US.
Those on diets high in monounsaturated fats, including oleic acid from olive oil, had lower rates of heart disease.
The seven-country study was the first to definitively link saturated fat intake to total cholesterol levels and heart disease.
Many of the modern dietary recommendations on fat intake are based on this study. Men and women in the “seven countries study” with elevated cholesterol levels had an increased risk of death from heart disease.
These protective effects are largely due to a decrease in total blood cholesterol levels, especially the “bad” low-density lipoprotein-cholesterol.
Limited evidence from an 8-week study of 23 patients at high risk for heart disease connects a diet high in monounsaturated fats with other protective functions of the heart (blood clotting and circulation).
Because oleic acid also acts on insulin sensitivity, blood pressure, inflammatory markers, and blood vessel function, those who consume it are protected against heart disease.
Oleic acid also lowered cholesterol levels in a study of 180 patients randomly assigned to diets high and low in monounsaturated fats for 2 years.
Oleic acid lowers blood pressure
In a study of 23 patients with elevated blood pressure, those assigned to diets high in monounsaturated fats had significantly reduced blood pressure after 6 months. Eight patients were able to stop taking blood pressure medications completely while on the diet.
However, the drop in blood pressure observed in that study of 23 patients was also related to a reduction in the consumption of saturated fats and an increase in nitric oxide levels stimulated by polyphenols present in olive oil, not only by the high in monounsaturated fats.
Rats with high blood pressure fed a different form of oleic acid (bioactive 2-hydroxyoleic acid) lowered their blood pressure to normal levels after 7 days of treatment.
These effects were attributed to changes in the production of proteins that control blood vessel contraction (increased PKA and decreased Rho A kinase proteins).
The integration of oleic acid into cell membranes can alter their structure to allow certain receptors to be present or absent on the membrane (G-protein-coupled receptors, specifically members of the adrenergic receptor family).
Increased levels of oleic acid in the vessels of rats fed a diet rich in olive oil was associated with an increase in blood pressure-lowering receptors (via PKA).
Oleic acid improves insulin sensitivity
When a group of adults (162 healthy people) received a diet high in saturated fat for 3 months, their insulin sensitivity decreased, compared to a group high in monounsaturated fat.
Ten overweight patients with non-insulin dependent diabetes improved their glycemic profiles (correlation of blood glucose and insulin value) when they received a diet high in monounsaturated fats for 15 days.
In mice with diet-induced diabetes and obesity, replacing oleic acid with saturated fat in the diet improved symptoms (hypothalamic inflammation, insulin resistance, and body fat).
Eleven pre-diabetic patients were fed 3 diets, each for 28 days, a diet high in monounsaturated fat, another high in saturated fat, and a third in carbohydrates. These patients had less abdominal fat and better insulin sensitivity on a diet high in monounsaturated fats.
Oleic acid prevents obesity
According to the World Health Organization, a diet high in monounsaturated fats was the best predictor of low obesity rates worldwide.
A 28-day diet high in monounsaturated fat reduced abdominal (core) fat, which is associated with obesity, in 11 insulin-resistant patients.
Obese mice injected directly with oleic acid into the hypothalamus reduced food intake and fat gain and improved symptoms associated with obesity, such as hypothalamic inflammation and body fat.
Oleic acid can improve the immune system and resolve inflammation
Oleic acid is incorporated into cell membranes and can interact directly with immune cells (neutrophils) responsible for controlling the duration and intensity of tissue inflammation.
Part of the inflammatory response in the human body requires the formation of reactive oxygen species by neutrophils at the site of inflammation. This recruits other molecules necessary for healing.
This response is increased in the presence of oleic acid leading to a more rapid resolution of inflammation, including the release of cytokines (IL1-b).
Neutrophils are also responsible for the identification and defense of pathogens. They more efficiently immersed (phagocytosed) and killed microorganisms when incubated with oleic acid.
Neutrophil recruitment to the site of inflammation increased when oleic acid was present in lung-injured model mice but decreased when tested in cells outside the body in a second study.
Therefore, it is not clear when or where oleic acid can help with this early response to inflammation.
Oleic Acid May Help With Rheumatoid Arthritis
Forty-three rheumatoid arthritis patients who received a dietary supplement of fish oil (high in omega-3) and olive oil (high in oleic acid) had the best improvements in pain and mobility compared to fish oil alone or a placebo (soybean oil).
Oleic Acid May Decrease Chronic Nerve Pain
Oleic acid inhibits a receptor (TRVP1) involved in the perception of pain (detection of spicy, hot temperatures and itching). This is part of the natural role of oleic acid in inflammation.
Injection of oleic acid and albumin at the injury site in mice reduced pain and involuntary movements associated with paralysis after spinal injury.
Albumin and oleic acid also promoted the growth of new (dendritic) nerve cells in normal mice and in mice genetically engineered to have human TRVP1.
Oleic acid injections in a mouse pain model reduced pain and inflammation similar to those seen in human arthritis patients.
Oleic acid is essential for brain function
Oleic acid is produced during nerve repair (mature axons) and plays a role in the production of myelin.
Adrenoleukodystrophy, a rare genetic disorder that leads to the breakdown of myelin, can be treated with a mixture of fatty acids, including oleic acid, to slow the disease rate and reduce brain inflammation.
Oleic acid improves mood
A small 3-week study (of 14 to 18 people per test group) linked a diet rich in oleic acid with higher energy expenditure at rest (mitochondrial activity), lower levels of anger, and increased physical activity.
In 20 adolescent boys with Attention Deficit Hyperactivity Disorder, blood oleic acid levels were positively related to brain plasticity and to openness and extraversion of children’s personalities.
Oleic acid decreases age-related cognitive decline
High consumption of monounsaturated fats was correlated with a lower risk of cognitive decline in a survey of more than 5,000 Italian older adults (over 65 years of age).
This lower risk is probably due to the role of oleic acid in maintaining the structural integrity of neurons. The brain’s need for monounsaturated fatty acids increases with age in rats.
Oleic acid can slow aging
Long-lived species like humans typically have higher levels of oleic acid in their membranes than shorter-lived species like rodents.
Aging is often related to oxidative stress on cell membranes and DNA damage caused by free radicals released during energy production (glycolysis and electron transport).
Rats that consumed more olive oil and probably have more oleic acid in their membranes had less age-related oxidative stress because these fatty acids are less susceptible to free radical damage.
Oleic acid can prevent cancer
Oleic acid’s ability to decrease oxidative stress in the cell and thus protect DNA from oxidative damage also reduces the risk of cancer.
Two studies interviewed more than 5,000 women with and without breast cancer about their eating habits. Women with high levels of oleic acid in their diets were less likely to have cancer.
Mice with induced lung cancer (adenocarcinoma) fed a diet rich in oleic acid had higher survival rates and longer disease-free periods.
However, mice with salivary gland tumors fed a diet rich in oleic acid increased tumor progression, possibly due to a lack of other monounsaturated fats in the diet.
Negative effects
Oleic acid at very high levels is bad
Omega-9 concentrations (expressed as a percentage of the cell membrane) in the red blood cells of 3,000 patients were correlated with the risk of death after 10 years.
The relationship was non-linear (U-shaped), indicating that low and high levels of omega-9 could increase the risk of heart failure and death, with an optimal level close to 14% of the red blood cell membrane (low levels less than 13% and high levels greater than 15% of the content of the cell membrane).
Mice fed an exclusively omega-9 diet developed deficiencies in necessary fatty acids (linoleic and alpha-linolenic acids used to build omega-3 and omega-6 fatty acids).
Converting a single diet to a single source of fat can be detrimental.
Oleic acid can have negative effects on reproduction
In mice, increased dietary intake of omega-9 fatty acids (such as oleic acid) has been linked to poor reproductive outcomes, including smaller litters of puppies and shorter gestation periods.
This is probably due to changes in the synthesis of steroid hormones during pregnancy.
When mothers consumed diets high in oleic acid during pregnancy, reduced sperm count and motility were observed in male offspring due to increased DNA damage (fragmentation and oxidative stress) in mice.
Oleic acid may not play a role in skin care
Oleic acid is often marketed as an ingredient in skin care products.
But there is little scientific evidence to support positive claims about UV (ultraviolet) damage prevention, free radical scavenging, or other skin benefits, either as a dietary supplement or in topical applications.
Limitations and Warnings
Dietary studies include many factors
Many of the dietary studies on monounsaturated fats use olive oil as a source of oleic acid.
This does not distinguish between omega-9 fatty acids (such as oleic acid) or other monounsaturated fatty acids (such as omega-3 or omega-6). Other compounds present in olive oil and other monounsaturated fatty acids in diets also have positive health effects.
Determining which components contribute the most to those effects can be very difficult without closely controlled studies, especially when the diets were self-reported by the participants.
Men and women respond differently
Population (epidemiological) studies often did not distinguish between men and women, and many intervention studies had exclusively male participants.
Where data for men and women were analyzed separately, the effects on blood cholesterol levels were often lower in women than in men.
